1. Field of the Invention
The pesent invention is for semi-conductor filters. Specifically this invention is for a multi-color tunable filter using epitaxial layers.
2. Description of the Prior Art
Modern electromagnetic spectrum studies permit identification of objects by characteristic frequency signatures. In particular, target emission in the infrared region appears to be highly reliable as a means of identifying targets.
Previous detectors have not permitted rapid scanning of several colors. To cover a portion of the spectrum, numerous detectors tuned to narrow adjacent bandwidths have had to be used. Each detector has a predetermined band gap energy. Light whose energy matches this amount is absorbed according to the photoelectric effect, E=(hc/.lambda.), where E is the band gap energy, h is Plank's constant, .lambda. is the wavelength of the light in question, and c is the speed of light.
It is also possible to communicate by discrete frequency shifts. However, present lasers can selectively shift frequencies at a faster rate than current receivers can decode. Thus, present receivers limit the rate of communication.